| 摘要 |
PROBLEM TO BE SOLVED: To provide an image reading lens which is bright and exhibits satisfactory optical performance even in such a wide viewing angle area that a half viewing angle exceeds 25 degrees in spite of compact constitution. SOLUTION: The image reading lens 25A comprises, in order from an object side, a negative first lens L1 that has a meniscus shape turning its concave surface to the object side, a second lens L2 that has a biconvex shape, a diaphragm S5, a positive third lens L3 that has a meniscus shape turning its convex surface to an image side, and a negative fourth lens L4 that has a meniscus shape turning its concave surface to the object side. The image reading lens 25A is constituted to satisfy 2.4<f3/f<3.5 and 0.07<D2/f<0.028 when the focal length of the entire system is defined as f, the focal length of the third lens L3 is defined as f3, and a distance between the image-side lens surface S2 of the first lens L1 and the object-side lens surface S3 of the second lens L2 is defined as D2. COPYRIGHT: (C)2009,JPO&INPIT
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